The present invention concerns a tubular connection, and in particular concerns a mechanically joined tubular connection having improved strength and fatigue resistance.
Load bearing members can be interconnected in a number of different ways. However, it is not always satisfactory to use separate fasteners since fasteners add cost and further require a separate, sometimes tedious, subassembly operation. Further, most fasteners create non-uniform stress distributions on the load bearing members at the connection. This results in high stress areas on the load bearing members potentially leading to premature failure of the load bearing members unless the members are substantially "beefed up" for heavy duty service. However, "beefed up" parts for heavy duty service can add substantially to part cost and weight, both of which are particularly undesirable in the competitive automotive industry. Further, heavy duty parts do not necessarily resolve the failure problems, particularly where the failure is by cyclical loading and fatigue.
Other mechanical fastening methods are also often not satisfactory. For example, press-fitting and/or clinching may not provide the tensile (pull-out) strength desired in the connection, particularly under cyclical loading. Non-mechanical fastening methods are also often not acceptable. For example, welding can cause non-uniform stress distribution in which case the welded assembly is sensitive to fatigue failure. Further, welding requires the use of skilled labor and close quality control to control variations in weld strength.
One known patent, U.S. Pat. No. 4,419,804 to Axthammer, discloses a method including inwardly hammering an outer tube onto an inner pin. However, this process requires a complex tool with multiple moving parts, which tool may not have the long-term durability or consistency desired when manufacturing a high volume part. Further, the material of the outer tube is not flowed uniformly onto the inner pin, but instead is hammered by repeated hits onto the inner pin, which hammering moves the material in small increments. The hammering method would necessarily be quite loud, and further may undesirably affect the outer tube material properties.
Thus, a tubular connection having improved strength and uniformity of stress distribution and also a method of manufacture solving the aforementioned problems is desired.